Aging is associated with declines in both cellular and humoral immunity. A consistent observation of the aging immune system is a change in T cells. Another possible mechanism of diminished cellular immunity associated with age includes accelerated lymphocyte apoptosis. Enhanced lymphocyte apoptosis may play an important role in the pathogenesis of HIV disease. This study will use healthy volunteers to confirm and expand upon such observations. Samples from these volunteers will serve as controls to those from the HIV-infected participants of A5015 (a comparison study of 2 age-differentiated cohorts to determine potential mechanisms that might contribute to accelerated HIV-disease progression that is associated with aging).